[C#] [DuckDb] Attaching multiple arrow streams without fully materialising

### What would you like help with?

I'm using ADBC in C# with the DuckDB driver. I had a good look through the source code, but I couldnt find a way of attaching multiple arrow streams without them being fully materialised first. I'd like to attach streams "a" and "b" (with dfferent schemas), and then only materialise them when the query "select * from a join b.." is executed. Is this possible? It looks like CreateStatement only supports binding a single stream.

I thought a workaround might be to use the duckdb C bindings and call out to duckdb_arrow_scan but I cant see a way of getting a handle to the underlying duckdb connection.